[RFC PATCH v5 25/38] KVM: arm64: VHE: Change MDCR_EL2 at world switch if VCPU has SPE

[Alexandru Elisei <alexandru.elisei@xxxxxxx>]

When a VCPU has the SPE feature, MDCR_EL2 sets the buffer owning regime to
EL1&0. Write the guest's MDCR_EL2 value as late as possible and restore the
host's value as soon as possible at each world switch to make the profiling
blackout window as small as possible for the host.

Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
 arch/arm64/kvm/debug.c          | 14 ++++++++++++--
 arch/arm64/kvm/hyp/vhe/switch.c | 15 +++++++++++++--
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 64629b4bb036..ee764ea0da5b 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -249,9 +249,19 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 		vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 
 	/* Write mdcr_el2 changes since vcpu_load on VHE systems */
-	if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
-		write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
+	if (has_vhe()) {
+		/*
+		 * MDCR_EL2 can modify the SPE buffer owning regime, defer the
+		 * write until the VCPU is run.
+		 */
+		if (kvm_vcpu_has_spe(vcpu))
+			goto out;
+
+		if (orig_mdcr_el2 != vcpu->arch.mdcr_el2)
+			write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
+	}
 
+out:
 	trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
 }
 
diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index f85a13bfad3d..1a46a4840d17 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -35,6 +35,9 @@ static void __activate_traps(struct kvm_vcpu *vcpu)
 {
 	u64 val;
 
+	if (kvm_vcpu_has_spe(vcpu))
+		__restore_guest_mdcr_el2(vcpu);
+
 	___activate_traps(vcpu);
 
 	val = read_sysreg(cpacr_el1);
@@ -70,6 +73,9 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
 {
 	extern char vectors[];	/* kernel exception vectors */
 
+	if (kvm_vcpu_has_spe(vcpu))
+		__restore_host_mdcr_el2(vcpu);
+
 	___deactivate_traps(vcpu);
 
 	write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
@@ -82,6 +88,7 @@ static void __deactivate_traps(struct kvm_vcpu *vcpu)
 	asm(ALTERNATIVE("nop", "isb", ARM64_WORKAROUND_SPECULATIVE_AT));
 
 	write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1);
+
 	write_sysreg(vectors, vbar_el1);
 }
 NOKPROBE_SYMBOL(__deactivate_traps);
@@ -89,12 +96,16 @@ NOKPROBE_SYMBOL(__deactivate_traps);
 void activate_traps_vhe_load(struct kvm_vcpu *vcpu)
 {
 	__activate_traps_common(vcpu);
-	__restore_guest_mdcr_el2(vcpu);
+
+	if (!kvm_vcpu_has_spe(vcpu))
+		__restore_guest_mdcr_el2(vcpu);
 }
 
 void deactivate_traps_vhe_put(struct kvm_vcpu *vcpu)
 {
-	__restore_host_mdcr_el2(vcpu);
+	if (!kvm_vcpu_has_spe(vcpu))
+		__restore_host_mdcr_el2(vcpu);
+
 	__deactivate_traps_common(vcpu);
 }
 
-- 
2.33.1

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